The present invention relates to fluid infusion systems, and more particularly to an improved apparatus for accurately metering the flow rate of fluid through an administration set.
The infusion of fluids such as parenteral solutions and blood into the human body is usually accomplished by means of an administration set in conjunction with metering means for controlling the rate of fluid flow through the set. One form of metering means which is attractive for this application is the peristaltic-type pump, which operates to repeatedly and progressively compress and expand a section of tubing of the administration set so as to cause fluid to flow through the set at a controlled rate, thereby avoiding the need for direct contact with fluid and the attendant risk of contamination.
Because of its partial non-resiliency, tubing formed of vinyl and other thermal plastic materials commonly utilized in administration sets may permanently change its shape and size with time as a result of repeated stretch-compressive cycling, such as it inherent in the operation of a peristaltic-type pump, with the result that the rate at which fluid is delivered by the pump may undesirably vary with time. A system which minimizes the effects of stretch-compressive cycling for improved metering accuracy is described in U.S. Pat. No. 4,155,362, which issued to Thurman S. Jess on May 22, 1979, and is assigned to the present assignee. Basically this system provides for flow restriction means downline of the peristaltic pump to obtain a downline fluid pressure at the point of pump compression which assists in restoring the tubing to its original shape following compression. The flow restriction means perform the additional function of preventing gravity flow in the event the pump head is disengaged by causing a total occlusion of the tubing in the absence of upline pressure. This system has been successfully incorporated in the Model 2M8014 infusion pump manufactured by the Travenol Division of Baxter Travenol Laboratories, Inc., of Deerfield, Illinois.
An additional level of protection against irregular fluid flow is provided by the metering apparatus of the present invention, which monitors fluid pressure in the tubing downline of the occlusion station and interrupts operation of the metering apparatus and sounds an alarm in the event that the pressure rises above a predetermined maximum level, indicating that the tubing has been crimped or occluded between the metering apparatus and the patient.
Prior art systems relied on electrical switches mechanically coupled to a plunger spring-biased against the wall of the tubing and position-dependent on the pressure of the fluid therein for stopping operation of the pump in the event of an occlusion. Unfortunately, the relative insensitivity and inherent unpredictability of switching point of such mechanically-actuated switches to the relatively small pressure changes encountered in the system required setting the threshold level higher than desirable to avoid false alarms during normal operation. As a result, the sensitivity of such systems to occlusions was less than desirable. The present invention is directed to an improved system for detecting downline occlusions which overcomes these limitations on sensitivity.
Accordingly, it is a general object of the present invention to provide a new and improved fluid infusion system.
It is a more specific object of the present invention to provide a new and improved apparatus for infusing fluids into the human body with improved protection against blocked fluid flow.
It is another object of the present invention to provide new and improved metering apparatus for controlling the flow of fluid through the compressible tubing of an administration set wherein operation of the apparatus is interrupted and an alarm is sounded when the fluid pressure downline of the apparatus exceeds a predetermined operating range.